A novel pH-sensitive intelligent indicating label for accurately indicating the freshness of chilled meat and a preparation method and application thereof

Abstract

The application belongs to the technical field of livestock processing, and discloses a novel pH-sensitive intelligent indicating label for precisely indicating the freshness of chilled meat and a preparation method and application thereof. The preparation method comprises the following steps: taking metal chromium, benzoic acid, hydrofluoric acid and deionized water as raw materials, and preparing MIL-100Cr material by using a solvothermal method; stirring, reacting and drying the purple cabbage freeze-dried powder and the MIL-100Cr material to obtain ANs@MIL-100Cr composite nanoparticles; stirring the pectin, the ANs@MIL-100Cr composite nanoparticles, glycerol and water to obtain a film-forming solution; and preparing the novel pH-sensitive intelligent indicating label for precisely indicating the freshness of chilled meat by film-forming and drying the film-forming solution. The indicating label can precisely distinguish the freshness change of chilled meat in the chilled storage and transportation process, and has the characteristics of wide application range, high sensitivity, stable performance, safety and biodegradability.

Description

Technical Field

[0001] The present invention belongs to the technical field of livestock processing, and in particular relates to a novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat, and a preparation method and application thereof. Background Art

[0002] In 2022, my country's total livestock and poultry meat production reached 92.27 million tons, of which approximately 80% was fresh meat. Freshness is the essence of fresh meat, but during cold chain storage and transportation, fresh meat is susceptible to the effects of exogenous microorganisms and endogenous enzymes, which can degrade its freshness. According to the World Health Organization, approximately 120 million people worldwide become ill each year from ingesting stale fresh meat. Therefore, there is an urgent need to develop a convenient and rapid method for real-time assessment of the freshness of fresh meat, thereby addressing bottlenecks in the development of fresh meat in my country. By developing key processing technologies, my country can develop independent intellectual property rights, support improvements in the quality and efficiency of the fresh meat industry, and enhance the international competitiveness of Chinese meat companies.

[0003] In indicator labels, the earliest indicators used were chemically synthesized pigments including methyl red and bromocresol blue. Although chemically synthesized pigments have advantages such as stable properties, convenient production, and high cost-effectiveness, they have low safety. In recent years, ANs have been widely used as pH indicators in indicator labels due to their high safety and strong pH response ability. It has been confirmed that indicator labels constructed with ANs from different sources can achieve real-time monitoring of the freshness of fresh meat. The present inventors previously prepared indicator labels using beetroot and purple cabbage ANs as pH indicators, respectively, to achieve intelligent monitoring of the freshness of fresh beef and fresh mutton. However, through analysis of the research results of the present inventors and predecessors, it was found that the indicator labels had low sensitivity for monitoring the freshness of fresh meat, which was specifically manifested in weak color response intensity at the corresponding freshness level and poor response ability to freshness changes in the early stage of cold chain storage and transportation. The main reasons for this include: (1) ANs in indicator labels are easily affected by environmental factors and decompose; (2) the amount of volatile amines produced in the early stage of cold chain storage and transportation of fresh meat is relatively small. Therefore, in order to improve the sensitivity of indicator labels in monitoring the freshness of fresh meat during cold chain storage and transportation, it is necessary to start from improving the stability of ANs and the enrichment of volatile amines.

[0004] In recent years, the MIL-100Cr series of materials has garnered increasing attention for improving the stability of active materials and gas enrichment, thanks to their unique pore structure, specialized metal sites, and high stability. The pore structure of MIL-100Cr provides a suitable microenvironment for active materials, preventing them from losing activity in harsh environments. Furthermore, thanks to its multi-porous structure, the accessibility of loaded active materials to substrates is minimally affected.

[0005] In addition, MIL-100Cr has a large specific surface area (over 1980m 2 / g) and adjustable pore structure, making it widely used in gas enrichment. MIL-100Cr gas enrichment methods include physical enrichment and chemical enrichment. Physical enrichment is based on the interaction forces between MIL-100Cr and gas molecules, including van der Waals forces and dispersion forces. Since the enrichment heat in this process is very low, the interaction between MIL-100Cr and the gas is weak, and there is no breaking and formation of chemical bonds. Therefore, MIL-100Cr is easy to regenerate and the original structure can be maintained intact. Depending on the molecular structure of the gas, the chemical enrichment mechanism of MIL-100Cr on gas can be divided into electrostatic effects, open metal sites, acid-base effects, π-π stacking, hydrogen bonds and van der Waals effects. Different from physical enrichment, chemical enrichment of gas molecules by MIL-100Cr depends on the chemical reaction between its surface functional groups and gas molecules. Based on the excellent gas enrichment ability and structural adjustable performance of MIL-100Cr, in recent years, many scholars have made directional adjustments to the molecular structure of MIL-100Cr in gas rapid monitoring materials according to the conformation of the gas molecules being detected, and have achieved cm 3 / m 3 Therefore, by incorporating MIL-100Cr into indicator labels, it is expected that the sensitivity of traditional indicator labels in detecting the freshness of fresh meat during cold chain storage and transportation will be improved, and accurate differentiation of the freshness level of fresh meat can be achieved. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the existing technology, the primary purpose of the present invention is to provide a method for preparing a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat. The new indicator label is prepared by using ANs@MIL-100Cr constructed by MIL-100Cr loaded with ANs as a pH indicator and pectin as a carrier to achieve accurate distinction of the freshness of fresh meat.

[0007] Another object of the present invention is to provide a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh chilled meat, which is prepared by the above-mentioned preparation method and has the characteristics of precision, strong sensitivity and easy identification.

[0008] Another object of the present invention is to provide an application of the above-mentioned novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing a novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat comprises the following steps:

[0011] (1) 30-50 mg of metallic chromium, 75-95 mg of benzoic acid, 0.2-0.6 mL of 2 mmol hydrofluoric acid, and 2-6 mL of deionized water were mixed evenly and added to a stainless steel autoclave lined with polytetrafluoroethylene. The mixture was reacted at 150-250° C. for 80-100 h and then cooled to room temperature. The obtained product was washed with water and hot ethanol in sequence and finally vacuum dried to remove the ethanol molecules adsorbed in the pores to obtain MIL-100Cr material.

[0012] (2) 45-50 g of purple cabbage was placed in a tissue crusher and stirred for 3-5 min, and then acetic acid 2-4 times the mass of the purple cabbage was added, and the mixture was shaken for 12-16 h in the dark at a temperature of 3-5 ° C and a shaking rate of 30-50 r / min, and then centrifuged at 3000-4000 g and 4 ° C for 5-15 min to collect the supernatant; the supernatant was pre-frozen, and then vacuum freeze-dried at 5-15 Pa and -30--50 ° C for 20-30 h to form ANs freeze-dried powder; the ANs freeze-dried powder and the MIL-100Cr material obtained in step (1) were added to deionized water, stirred at a speed of 100-200 r / min in the dark for 5-7 h, and then vacuum freeze-dried at 20-30 Pa and -40--60 ° C for 30-40 h to obtain ANs@MIL-100Cr composite nanoparticles;

[0013] (3) Pectin and ANs@MIL-100Cr composite nanoparticles were added to deionized water at a weight percentage of 3-5% and 0.1-0.3% respectively, and stirred at a rotation speed of 80-120 r / min and a temperature of 20-30°C for 25-35 min to obtain a film-forming liquid; the film-forming liquid was placed on a film-making plate, and the formed film was peeled off after drying to obtain a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh chilled meat.

[0014] The vacuum drying in step (1) is carried out under vacuum conditions of 20 to 30 Pa for 12 to 16 hours.

[0015] The pre-freezing in step (2) is performed at -18 to 20° C. for 4 to 6 hours.

[0016] In step (3), placing the film-forming liquid in the film-forming plate is to place 30 to 40 mL of the film-forming liquid in a 10×10 cm film-forming plate; the drying is to dry at 40 to 50° C. for 5 to 9 hours; and the obtained new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat is placed in a dark, cool and dry place for use.

[0017] A novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat is prepared by the above-mentioned preparation method.

[0018] The application of the above-mentioned new pH-sensitive intelligent indicator label in real-time and accurate monitoring of the freshness of fresh meat is characterized in that: the application includes the following steps: placing the fresh pork that has passed the quarantine in a packaging box, sticking the cut new pH-sensitive intelligent indicator label on the inner side of the upper cover of the packaging box, sealing the packaging box with a sealing film, and storing it at 4°C for 8 days. Observe the color changes of the new pH-sensitive intelligent indicator label to judge whether the fresh pork is fresh, sub-fresh, or corrupt.

[0019] The unique pore structure, special metal sites, high stability, and ultra-large specific surface area of ​​MIL-100Cr material make it an excellent material for improving the stability of active substances and gas enrichment. It has the potential to increase the sensitivity of traditional indicator labels for monitoring the freshness of fresh meat by improving the stability of ANs and enriching volatile amines, characteristic markers of freshness produced during the deterioration of freshness of fresh meat. However, in the existing technology, there is no report of using ANs@MIL-100Cr composite nanoparticles constructed by MIL-100Cr loaded with ANs as an indicator to prepare indicator labels.

[0020] The present invention has the following advantages and effects compared to the prior art:

[0021] (1) The preparation method of the MIL-100Cr material described in the present invention uses metallic chromium, benzoic acid, hydrofluoric acid and deionized water as raw materials and adopts a solvothermal method to prepare MIL-100Cr. The experimental conditions are mild and the reaction by-products are few, which meets the requirements of green manufacturing technology.

[0022] (2) The novel pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat of the present invention is a novel indicator label of ANs@MIL-100Cr / pectin, which can accurately distinguish the changes in the freshness of fresh meat during storage and transportation, and has the characteristics of wide application range, high sensitivity, stable performance, safety and biodegradability;

[0023] (3) The method for real-time detection of the freshness of chilled meat provided by the present invention is easy to operate, easy to identify, and sensitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of freshness monitoring of chilled pork using ANs@MIL-100Cr / pectin indicator label. DETAILED DESCRIPTION

[0025] The present invention is further described below with reference to specific examples, but these examples should not be construed as limiting the present invention.

[0026] Example 1

[0027] Metallic chromium (30 mg), benzoic acid (75 mg), 2 mmol hydrofluoric acid (0.2 mL) and deionized water (2 mL) were mixed evenly and added to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. The mixture was reacted at 150°C for 80 hours. After synthesis, the sample was cooled to room temperature. The resulting product was washed with water and hot ethanol in sequence, and finally dried under 20 Pa vacuum conditions for 12 hours to remove the ethanol molecules adsorbed in the pores to obtain MIL-100Cr material.

[0028] Example 2

[0029] A mixture of chromium (40 mg), benzoic acid (85 mg), 2 mmol of hydrofluoric acid (0.4 mL), and deionized water (4 mL) was added to a Teflon-lined stainless steel autoclave and reacted at 200°C for 90 hours. After synthesis, the sample was cooled to room temperature. The resulting product was washed sequentially with water and hot ethanol, and finally dried under a vacuum of 25 Pa for 14 hours to remove ethanol molecules adsorbed in the pores, yielding the MIL-100Cr material.

[0030] Example 3

[0031] A mixture of chromium metal (50 mg), benzoic acid (95 mg), 2 mmol of hydrofluoric acid (0.6 mL), and deionized water (6 mL) was added to a Teflon-lined stainless steel autoclave and reacted at 250°C for 100 hours. After synthesis, the sample was cooled to room temperature. The resulting product was washed sequentially with water and hot ethanol, and finally dried under 30 Pa vacuum for 16 hours to remove ethanol molecules adsorbed in the pores, resulting in the MIL-100Cr material.

[0032] Example 4

[0033] 40 g of purple cabbage was placed in a tissue crusher and stirred for 3 minutes. Then, acetic acid twice the mass of the purple cabbage was added, and the mixture was shaken for 12 hours in the dark at a temperature of 3°C and a shaking rate of 30 r / min. Then, the supernatant was collected after centrifugation at 3000g and 4°C for 5 minutes. The supernatant was pre-frozen at -18°C for 4 hours, and then vacuum freeze-dried at 5 Pa and -30°C for 20 hours to form ANs freeze-dried powder. The ANs freeze-dried powder and the MIL-100Cr material obtained in Example 2 were added to deionized water, stirred at a speed of 100 r / min in the dark for 5 hours, and then vacuum freeze-dried at 20 Pa and -40°C for 30 hours to obtain ANs@MIL-100Cr composite nanoparticles.

[0034] Example 5

[0035] 45 g of purple cabbage was placed in a tissue crusher and stirred for 4 minutes, and then acetic acid 3 times the mass of the purple cabbage was added, and the mixture was shaken in the dark at a temperature of 4°C and a shaking rate of 40 r / min for 14 hours, and then centrifuged at 3500g and 4°C for 10 minutes, and the supernatant was collected; the supernatant was pre-frozen at -20°C for 5 hours, and then vacuum freeze-dried at 10 Pa and -45°C for 25 hours to form ANs freeze-dried powder; the ANs freeze-dried powder and the MIL-100Cr material obtained in Example 2 were added to deionized water, stirred at a speed of 150 r / min in the dark for 6 hours, and then vacuum freeze-dried at 25 Pa and -50°C for 35 hours to obtain ANs@MIL-100Cr composite nanoparticles.

[0036] Example 6

[0037] 50 g of purple cabbage was placed in a tissue crusher and stirred for 5 minutes. Then, acetic acid 4 times the mass of the purple cabbage was added, and the mixture was shaken for 16 hours in the dark at a temperature of 5°C and a shaking rate of 50 r / min. Then, the supernatant was collected after centrifugation at 4000g and 4°C for 15 minutes. The supernatant was pre-frozen at -22°C for 6 hours, and then vacuum freeze-dried at 15 Pa and -50°C for 30 hours to form ANs freeze-dried powder. The ANs freeze-dried powder and the MIL-100Cr material obtained in Example 2 were added to deionized water, stirred at a speed of 200 r / min in the dark for 7 hours, and then vacuum freeze-dried at 30 Pa and -60°C for 40 hours to obtain ANs@MIL-100Cr composite nanoparticles.

[0038] Example 7

[0039] Pectin, 3%, 0.1% and 0.3% by weight of deionized water, the ANs@MIL-100Cr composite nanoparticles obtained in Example 5 and glycerol were added to deionized water, and the mixture was stirred at a speed of 80 r / min and a temperature of 20°C for 25 min to obtain a film-forming liquid; 30 mL of the film-forming liquid was placed on a 10×10 cm film-forming plate and dried at 40°C for 5 h. After drying, the formed film was peeled off to obtain a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat, which was placed in a dark, cool and dry place for use.

[0040] Example 8

[0041] Pectin, 4%, 0.2% and 0.5% by weight of deionized water, the ANs@MIL-100Cr composite nanoparticles obtained in Example 5 and glycerol were added to deionized water, and the mixture was stirred at a speed of 100 r / min and a temperature of 25°C for 30 min to obtain a film-forming liquid; 35 mL of the film-forming liquid was placed on a 10×10 cm film-forming plate and dried at 45°C for 7 h. After drying, the formed film was peeled off to obtain a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat, which was placed in a dark, cool and dry place for use.

[0042] Example 9

[0043] Pectin, 5%, 0.3% and 0.7% by weight of deionized water, the ANs@MIL-100Cr composite nanoparticles obtained in Example 5 and glycerol were added to deionized water, and the mixture was stirred at a speed of 120 r / min and a temperature of 30°C for 35 min to obtain a film-forming liquid; 40 mL of the film-forming liquid was placed on a 10×10 cm film-forming plate and dried at 50°C for 9 h. After drying, the formed film was peeled off to obtain a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat, which was placed in a dark, cool and dry place for use.

[0044] Example 10

[0045] The new pH-sensitive intelligent indicator label obtained in Example 8 is used to accurately monitor the freshness of fresh meat in real time, specifically comprising the following steps: 100 g of fresh pork that has passed quarantine is placed in a 5×5×3 cm packaging box, affixes the cut new pH-sensitive intelligent indicator label with a size of d=2.0 cm to the inner side of the upper cover of the packaging box, seals the packaging box with a sealing film, and stores it at 4°C for 8 days, observing the color change of the indicator label as the fresh pork changes from fresh to spoiled.

[0046] Example 11

[0047] The new pH-sensitive intelligent indicator label obtained in Example 8 is used to accurately monitor the freshness of fresh meat in real time, specifically comprising the following steps: 150 g of fresh pork that has passed quarantine is placed in a 5×5×3 cm packaging box, a new pH-sensitive intelligent indicator label with a cut size of d=2.5 cm is affixed to the inner side of the upper cover of the packaging box, the packaging box is sealed with a sealing film, and stored at 4°C for 8 days, and the color change of the indicator label as the fresh pork changes from fresh to spoiled is observed.

[0048] Example 12

[0049] The novel pH-sensitive intelligent indicator label obtained in Example 8 is used to accurately monitor the freshness of fresh meat in real time. Specifically, the following steps are included: 200g of fresh pork that has passed quarantine is placed in a 5×5×3cm packaging box, affix the new pH-sensitive intelligent indicator label with a size of d=3.0cm after cutting to the inner side of the upper cover of the packaging box, seal the packaging box with a sealing film, store it at 4°C for 8 days, and observe the color change of the indicator label as the fresh pork changes from fresh to spoiled. Figure 1 Analysis of color, TVB-N, pH, total bacterial count, and sensory evaluation data during cold storage of fresh pork, combined with the current national standard GB / T 9959.2-2008, showed that fresh pork reached the sub-fresh level on the fourth day and the spoilage level on the seventh day. As shown in Table 1, as the indicator label increased from the fresh to spoilage level, the label's brightness (L*) significantly decreased from 47.51±1.33 to 39.17±2.15 (P<0.05), the redness (a*) significantly decreased from 6.17±0.29 to 3.15±0.14, and the yellowness (b*) significantly decreased from 9.15±0.09 to 6.21±0.11. The indicator label also changed from light red to purple and finally to green, making it easily distinguishable to the naked eye. The above results show that the indicator label prepared with ANs@MIL-110Cr as pH indicator can accurately respond to the sub-freshness and corruption level of fresh pork, and realize accurate monitoring of the freshness of fresh pork throughout the storage and transportation process.

[0050] Table 1 Color difference values ​​of ANs@MIL-100Cr / pectin indicator labels at different freshness levels

[0051]

[0052] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat, characterized in that The following steps are included: (1) 30-50 mg of metallic chromium, 75-95 mg of benzoic acid, 0.2-0.6 mL of 2 mmol hydrofluoric acid, and 2-6 mL of deionized water were mixed evenly and added to a stainless steel autoclave lined with polytetrafluoroethylene. The mixture was reacted at 150-250° C. for 80-100 h and then cooled to room temperature. The obtained product was washed with water and hot ethanol in sequence and finally vacuum dried to remove the ethanol molecules adsorbed in the pores to obtain MIL-100Cr material. (2) 45-50 g of purple cabbage was placed in a tissue crusher and stirred for 3-5 min, and then acetic acid 2-4 times the mass of the purple cabbage was added, and the mixture was shaken for 12-16 h in the dark at a temperature of 3-5 ° C and a shaking rate of 30-50 r / min, and then centrifuged at 3000-4000 g and 4 ° C for 5-15 min to collect the supernatant; the supernatant was pre-frozen, and then vacuum freeze-dried at 5-15 Pa and -30--50 ° C for 20-30 h to form ANs freeze-dried powder; the ANs freeze-dried powder and the MIL-100Cr material obtained in step (1) were added to deionized water, stirred at a speed of 100-200 r / min in the dark for 5-7 h, and then vacuum freeze-dried at 20-30 Pa and -40--60 ° C for 30-40 h to obtain ANs@MIL-100Cr composite nanoparticles; (3) Pectin and ANs@MIL-100Cr composite nanoparticles were added to deionized water at a weight percentage of 3-5% and 0.1-0.3% respectively, and stirred at a rotation speed of 80-120 r / min and a temperature of 20-30°C for 25-35 min to obtain a film-forming liquid; the film-forming liquid was placed on a film-making plate, and the formed film was peeled off after drying to obtain a new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh chilled meat.

2. The preparation method according to claim 1, wherein: The vacuum drying in step (1) is carried out under vacuum conditions of 20 to 30 Pa for 12 to 16 hours.

3. The preparation method according to claim 1, wherein: The pre-freezing in step (2) is performed at -18 to 22° C. for 4 to 6 hours.

4. The preparation method according to claim 1, wherein: In step (3), placing the film-forming liquid in the film-forming plate is to place 30 to 40 mL of the film-forming liquid in a 10×10 cm film-forming plate; the drying is to dry at 40 to 50° C. for 5 to 9 hours; and the obtained new pH-sensitive intelligent indicator label for accurately indicating the freshness of fresh meat is placed in a dark, cool and dry place for use.

5. A novel pH-sensitive intelligent indicator label for accurately indicating the freshness of chilled meat, prepared by the preparation method according to claim 1.

6. Application of the novel pH-sensitive intelligent indicator label according to claim 5 in real-time and accurate monitoring of the freshness of chilled meat, characterized in that: The application includes the following steps: placing fresh pork that has passed quarantine in a packaging box, attaching a cut new pH-sensitive smart indicator label to the inner side of the upper cover of the packaging box, sealing the packaging box with a sealing film, storing it at 4°C for 8 days, observing the color change of the new pH-sensitive smart indicator label, and judging whether the fresh pork is fresh, sub-fresh, or spoiled.

Images